This section is intended to introduce various aspects of the art, which may be associated with exemplary embodiments of the present invention. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the present invention. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of prior art.
Many enhanced hydrocarbon recovery operations can be classified as one of the following types: pressure maintenance and miscible flooding. In a pressure maintenance operation, inert gasses such as nitrogen are injected into a primarily gaseous reservoir to maintain at least a minimal pressure in the reservoir to prevent retrograde condensation and improve total recovery. In a miscible flooding operation, miscible gasses such as carbon dioxide are injected into a primarily liquidous reservoir to mix with the liquids, lowering their viscosity and increasing pressure to improve the recovery rate.
Many oil producing countries are experiencing strong domestic growth in power demand and have an interest in enhanced oil recovery (EOR) to improve oil recovery from their reservoirs. Two common EOR techniques include nitrogen (N2) injection for reservoir pressure maintenance and carbon dioxide (CO2) injection for miscible flooding for EOR. There is also a global concern regarding green house gas (GHG) emissions. This concern combined with the implementation of cap-and-trade policies in many countries make reducing CO2 emissions a priority for these and other countries as well as the companies that operate hydrocarbon production systems therein.
Some approaches to lower CO2 emissions include fuel de-carbonization or post-combustion capture. However, both of these solutions are expensive and reduce power generation efficiency, resulting in lower power production, increased fuel demand and increased cost of electricity to meet domestic power demand. Another approach is an oxyfuel gas turbine in a combined cycle (e.g. where exhaust heat from the gas turbine Brayton cycle is captured to make steam and produce additional power in a Rankine cycle). However, there are no commercially available gas turbines that can operate in such a cycle and the power required to produce high purity oxygen significantly reduces the overall efficiency of the process. Several studies have compared these processes and show some of the advantages of each approach. See, e.g. BOLLAND, OLAV, and UNDRUM, HENRIETTE, Removal of CO2 from Gas Turbine Power Plants: Evaluation of pre- and post-combustion methods, SINTEF Group, found at http://www.energy.sintef.no/publ/xergi/98/3/3art-8-engelsk.htm (1998).
U.S. Pat. No. 4,344,486 (the '486 patent) discloses a process of adding substantially pure oxygen to the produced hydrocarbons and carbon dioxide from a liquid producing formation to produce heat or power and re-injecting the carbon dioxide for EOR. The '486 patent discloses separating hydrocarbon liquids from gaseous constituents in a production stream of a liquid producing formation, then mixing the gaseous constituents with substantially pure oxygen and combusting the mixture to produce heat and CO2. The CO2 is then injected into the same or a different liquid producing formation. This approach fails to teach or suggest a solution to the efficiency drag from the oxygen plant.
U.S. Pat. Pub. No. 2007/0237696 (the '696 publication) discloses essentially a combination of the oxy-fuel process and EOR as disclosed in the '486 patent. The '696 publication also requires a stand-alone oxygen plant or air separation plant, and fails to teach or suggest a working gas power turbine configuration.
More recently International Patent Application no. US2009/038247 discloses a system that provides a solution to the efficiency drag from the oxygen plant and further provides an inert gas (nitrogen) injection for reservoir pressure maintenance. In the integrated system of US2009/038247, however, the net power produced is generally reduced by the power consumption requirement of the process even at the improved efficiency.
As such, there is still a substantial need for a low emission, high efficiency hydrocarbon recovery process with increased power production.